Electronic equipment systems employ clock sources to control the timing of logic components within the systems. In traditional systems, a clock generation module or card is employed on the backplane of the system to distribute timing signals through the backplane to each chassis card. The clock generation module may include an oscillator crystal driving a phase-locked loop. The clock generation module may also possess various filtering circuits and clock duplication functionality. From the clock generation module, the clocks are distributed to the other cards of the system to control the timing of logic events.
Additionally, in more complex systems, it is often advantageous to connect multiple backplanes. To coordinate the timing between backplanes, it is typical to provide a coaxial or other cable from a timing unit on a first backplane to a timing unit on the second backplane. The coaxial cable is used to communicate a timing signal generated by the timing unit on the first backplane. The timing unit on the second backplane synchronizes to the received timing signal. Accordingly, the clocks distributed to devices of the second backplane by the second timing unit are synchronized to the clocks distributed to devices of the first backplane.